To obtain more efficient medication, multiple biodegradable materials were developed for drug delivery carrier, such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactid-co-glycolide) (PLGA) and poly(alkyl-cyanoacrylate) (PACA). Therapeutic agents, particularly anti-cancer drugs, might undergo degradation gradually or cause systemic side effects through intravenous injection or oral administration. Patients not only seriously suffered but also received insufficient therapeutic drugs. While encapsulated in the nanoparticles, these drugs were fully protected by polymers and possessed high stabilities in the in vivo and in vitro studies. In addition, by modulating compositions of the nanoparticles, the drug-loaded particles might be delivered to target cells or tissues and achieve the specificity of treatment. Therefore, biodegradable nanoparticles were used extensively.
Biodegradable PACA had developed as an effective drug delivery device for sustained and localized administration of various pharmacologically active agents, such as cytotoxic drugs, antibiotics, peptides, and genes. For therapeutic use, the drug-loading efficiency of nanoparticles must be maximized in order to minimize the amount of carrier. According to the previous studies, PACA nanoparticles with porous structure possessed a highly specific area on which various quantities of agents were adsorbed. The formed nanoparticles obtained the capability of encapsulating a wide range of drugs, and their non-solvent clear manufacturing process allowed them as the effective drug delivery device.
Conventional techniques for preparing drug-loaded PACA nanoparticles were by anion emulsion polymerization process in surfactant-containing acidic aqueous solution. The capsulated drugs, dissolved in the medium during or after polymerization, were stable reserved in the nanoparticles. However, the delivery system composed of PACA had low loading efficiency for poorly water-soluble drugs. There were several strategies used to increase the carrier capacity, such as selection of stabilizer, adjustment of pH of the medium, the amount and time of drug addition or modulating hydrophilic/hydrophobic properties of polyalkylcyanoacrylate. However, the maximum weight of the entrapped drug was limited to that dissolved in the medium.
Paclitaxel was a quite effective chemotherapeutic agent and had been clinically applied to treat a wide range of tumors, such as ovarian cancer, breast cancer, bladder cancer, esophagus cancer, melanoma and leukemia. Paclitaxel was used, in general, in the form of self-emulsifying system due to its fairly low water solubility (less than 3 ng/ml). Therefore, the solubilization technique of this drug had been developed along with the drug itself, particularly for systemic administration. The solubilization technique was the use of solubilizing agents, such as Cremophore EL (polyethoxyethylene 35 castor oil), polyoxyethoxylated castor oil and dehydrated alcohol. Before clinical administration, paclitaxel dissolved in solubilizing agents was dispersed in excess amount of normal saline or dextrose solution (5%). However, these solubilizing agents had serious toxic side effects. Cremophore EL, for instance, caused hypersensitivity, neurotoxicity, enphorotoxicity and cardiotoxicity. In present studies, biodegradable polymeric micro/nanoparticles, liposomes, core/shell nanoparticles, micelles or dendritic polymers were utilized for the construction of paclitaxel-loaded nanoparticles.
As described above, the drug-delivery nanoparticles composed of PACA encapsulated hydrophobic agents with low loading efficiency. In the preparation process of the therapeutic nanoparticles by conventional emulsion polymerization, drugs were dissolved in the polymerization medium before introducing monomer or added after the polymerization so that drugs were encapsulated during polymerization or adsorbed in the particles. Hence, the solubility of drug in the polymerization medium decided the amount of drug encapsulation. It seemed impracticable to obtain paclitaxel-loaded PACA nanoparticles with high loading efficiency by conventional emulsion polymerization, due to the low water solubility of paclitaxel. Furthermore, in conventional emulsion polymerization, the active molecules were transported slowly or sparsely through the water phase and onto the growing reaction sites, especially for those highly hydrophobic agents. Eventually, it would result in large amount of precipitate and aggregate. The produced nanoparticles were not only with low encapsulation efficiency of the encapsulants, while the waste of active agents was significant as well.
In view of the limitation of prior process of PACA emulsion polymerization, it would be desirable to produce nanoparticles with high stability and high loading/encapsulation efficiencies for hydrophobic agents. It would be desirable to preclude the reaction materials from further wasting.